1. Field of the Invention
The present invention relates to aerobic wastewater treatment systems and, more particularly, to an aeration vessel for use in such systems.
2. Description of Prior Art
Aerobic wastewater treatment systems are generally comprised of three main vessels, a trash or pretreatment vessel, an aeration vessel, and a pump tank. In a typical system, wastewater from a residence, industrial facility, or the like, passes into the pretreatment tank where most of the solids settle out. The effluent from the pretreatment tank then flows into the aeration vessel wherein remaining solids are subjected to aerobic digestion to provide a substantially solids free effluent which then passes into the pump tank for discharge. It is common for the aeration vessel to include an inverted frustoconical partition disposed in the aeration vessel which effectively divides the aeration vessel into an aeration chamber and a clarifier chamber, an oxygen-containing gas being introduced into the aeration chamber, substantially clarified water passing from the clarifier chamber into the pump tank.
Typical aeration vessels can be made of concrete, fiberglass, steel, etc., and can be rectangular, cylindrical, etc. Many aeration vessels are made of compositors comprised of fiberglass or similar reinforcing material(s) and a resin, e.g., epoxy, phenolic, etc., and are generally cylindrical in nature.
Because of the volume of the tanks, e.g., typically 400 to 1000 gallons, the vessels are quite large and bulky to ship.
Aside from being bulky in terms of shipping or transporting the aeration vessels to the desired location, aeration vessels made of composites, have a tendency to be somewhat buoyant with the result that in areas with high water tables or in ground which is highly saturated, they become buoyant enough to have a tendency to at least partially float.
Another problem with aeration vessels, particularly cylindrical type, made of composites is that, once in place in the ground, forces acting externally of the vessel by the surrounding earth, can cause the vessels to form cracks at approximately the middle region where the vessel is weakest in terms of having any supporting members to counteract the forces acting on the vessel in that region. In this regard, the bottom and top of the vessel are adequately supported against external, generally radially acting pressure, since the bottom wall and the top wall effectively act as reinforcing ribs.